Since it is reported that in the absence of cell surface protease TMPRSS2, SARS-CoV can achieve cell entry via an endosomal pathway in which it can be activated by other proteases such as cathepsin L (31), we further investigated gene expression dynamics of the endosomal cysteine proteases, cathepsins and found out that CTSB, CTSD, and CTSL were up-regulated significantly in CMs during HF (Figure 4D). Here, CTSB is linked to hydrops fetalis.